Interaction between a dislocation and various divalent impurity in KCl single crystals for the Fleischer's model taking account of the Friedel relation

Abstract

The interaction between a dislocation and the impurity in KCl : Mg2+ (0.035 mol% in the melt), KCl : Ca2+ (0.035 and 0.065 mol% in the melt) and KCl : Ba2+ (0.050 and 0.065 mol% in the melt) was investigated from the strain-rate cycling test during the Blaha effect measurement. This was carried out at 77–254 K. As a result, it was found that the Fleischer's model taking account of the Friedel relation seems to be suitable for KCl : Ca2+ and KCl : Ba2+. However, it was not appropriate for KCl : Mg2+. Furthermore, the values of Tc, ΔH(Tc) and ΔG0 were obtained for the specimens. Tc is the critical temperature at which effective stress is zero. ΔH(Tc) and ΔG0 are the enthalpy and the Gibbs free energy of activation for the breakaway of the dislocation from the impurity, respectively. ΔH(Tc) was almost the same for the specimens except KCl : Mg2+. ΔG0 increased with increasing the divalent cation size. In addition, the tetragonality around the divalent ion-positive ion vacancy pair was estimated on the basis of ΔG0 for the each specimen.